The present invention relates to an arc stud welding device and method using an arc discharge in which electric power is applied between a welding component such as a stud, nut or tube, and a welded component, such as a car body or metal panel, in order to generate an arc, melt the welding component and a portion of the welded component, and weld the welding component to the welded component.
So-called drawn arc stud welding is well known. In this type of arc discharge stud welding, electric power is applied between a welding component such as a stud and a welded component such as a car body, a low current pilot arc followed by a high current main arc are generated between the welding component and welded component separated from one another, and the welding component is welded to the welded component.
One type of arc stud welding device is disclosed in Unexamined Patent Application Publication (Kokai) No. 07-009146 (Patent Document 1). In the device described in Patent Document 1, a linear motor is used in the welding tool, the configuration of the welding tool holding the stud is simplified, and the positioning of the stud over the welded component is made easier. As described in Paragraphs 0025 and 0026 of Patent Document 1, the linear motor is operated so as to raise the welding component from a reference plane of the welded component to a pre-determined height, an arc is generated between the components, and the melted tip of the welding component is pressed into the melted portion of the welded component to a predetermined sink-in depth.
In Unexamined Patent Application Publication (Kokai) No. 07-136766 (Patent Document 2), a circuit is installed to detect contact between a stud and a welded component, and the contact between the stud and the welded component is monitored to ensure the start of welding. In Unexamined Patent Application Publication (Kokai) No. 11-077310 (Patent Document 3), the lift-up distance for a stud with respect to a welded component and the push-in depth for the stud with respect to the welded component after the lift up, are preset, the lift-up distance and push-in depth are monitored to determine whether or not they are within the tolerances for preset values, and the pass or fail quality of the welding is checked. In Unexamined Patent Application Publication (Kokai) No. 05-000376 (Patent Document 4), a stud welding device is disclosed that is able to weld a stud to various types of welded components with different shapes. Correction control is performed by feed-back of the amount of movement to position the stud in the welding tool over a predetermined position on the welded component.
Generally, in arc stud welding, the welding component is pressed into a portion of the welded component, and electric power is applied to the welding component and the welded component in contact with one another. A linear motor is operated to lift the welding component from the welded component, an arc is generated, and a tip of the welding component and the welded portion of the welded component are melted. The welding component is then pressed into the welded component, and the welding component is welded to the welded component. Since the welding component is forcibly brought into contact with the welded component at the start of the welding operation, if the welded component is not sufficiently rigid, the pressure applied to the welded component may cause it to become bowed or bent, forming a depression, and cause the welded component to sink to a sink-in depth below its original welded plane.
When the welding component is lifted for generating the arc, the welding component is usually lifted to a predetermined height above the position where the welding component came into contact with the welded component. However, if the applied pressure has caused the welded component to become bowed or bent, it may return to its original plane when it is no longer under pressure. Lifting of the welding component to the predetermined height from the bowed or bent position may not be sufficient to permit generating a proper arc, which may cause defective welding. When the sink-in depth is greater than the predetermined lift-up height, the rebound of the welded component causes the welding component to remain in contact therewith even after the welding component has been lifted. Thus, an arc cannot be generated. Patent Documents 1 through 4 do not meaningfully address this problem.
Also, when the welded component is not sufficiently rigid and sinks below its original plane, the welding component may not apply sufficient pressure to the welded component until the sink-in depth is reached, which may cause defective welding. Patent Documents 1 through 4 do not meaningfully address this problem.
A tube-shaped component called a flash shield may be placed around the head on the welding tool in an effort to hold the lift-up distance and the sink-in distance constant. Space is needed for a flash shield of fixed size to make contact with the portion of the welded component to be welded, but proper welding cannot be performed if the location or shape of that portion of the welded component does not provide enough space to accommodate the flash shield.